Safety control apparatus for fuel burners



June 26; 1945. Q K, STRQBEL I 2,379,114

SAFETY CONTROL APPARATUS FOR FUEL BURNERS Filed Feb. 9, 1942 TIME 062A),RELAV 77/115 DELAY CUT-OUT coma/-50 VAL v5 AND SWITCH 1N VEN 1 OR.

CHARLES KSTRoBEL.

ATTORNEK Patented June 26, 1945 SAFETY CONTROL APPARATUS FOR FUELBURNERS Charles K. Strobel, Pittsburgh, Pa., assignor to RobertshawThermostat Company, Youngwood, =Pa., a corporation of PennsylvaniaApplication February 9, 1942, Serial No. 430,002

13 Claims.

This invention relates to safety controls. for fuel burners and, moreparticularly to electrically operated controls therefor.

Electrically operated fuel control apparatus has been arrangedto permitsupply of gaseous fuel to a main burner if a heat or flame sensitiveportion of the apparatus has previously been heated by a pilot burner.The flame sensitive device may take the form of an electrical resistanceelement having the characteristic of changing its resistance when heatedand thus changing the value of the energizin current supplied to thefuel controlling member of the safety apparatus. The use of the variableresistance characteristic of the flame sensitive device, not only tohold the fuel controlling member open but also to cause its actuation tosuch position, introduces objectionable features. The establishment offlame sensitive circuit conditions may. however, be used as a device formaintaining flow of fuel to the burner, provided such flow is notinitiated thereby.

Apparatus of this type lends itself conveniently to the use ofelectrical igniting devices for the burner. Where ignition elements ofthe hot-wire type are employed it is desirable to remove such elementsfrom the circuit, as by deenergization thereof, after the burner isignited. Such treatment assists in prolonging the life of these elementsbeyond that expected when continuous energization is employed.

It is an object of this invention to establish a condition in anelectrical safety control apparatus for determining whether fuel flow tothe burner shall continue when the igniter is removed from the rcuitafter ignition should have occurred.

Another ct of the invention is to ensure positive operation the fuelflow controlling member while leaving it fully responsive to thecondition of the flame sensitive device.

Another object of the invention is to prolon the life of the ignitingelement.

Another object of the invention is to avoid reliance on the provision ofa pilot burner and percontrol apparatus for a gaseous fuel burnerembodying this invention.

Referring more particularly to the drawing, a gaseous fuel burner 10 issupplied with fuel by a main fuel pipe I2. The fuel supply is controlledby a main valve M which, in thisinstance, is arranged for manualoperation but which may be arranged for thermostatic operation ifdesired. Interposed in the fuel supply pipe l2 between the main valve Idand the burner i0 is an electromagnetic or solenoid gas valve I6 of anyknown type which may be arranged, as in this instance,

to be opened by energization of the solenoid and closed by gravity upondeenerization thereof.

Electric current for the operation of the apparatus is supplied by theline wires It connected to the primary of a transformer 20. It is desirable in such apparatus that the electric cur-- invention the safetycontrol and ignition system is illustrated and described as operatingdirectly upon the main burner Hi. It will be understood, however, thatwhile the apparatus lends itself to such arrangement it is equallyapplicable to systems employing a pilot burner also. In such cases thepilot burner could receive its supply of fuel from the fuel pipe l2either ahead of the solenoid valve id or from between this valve and themain burner l0. Such choice of pilot connection depends upon whethercomplete shut-off of fuel is desired in case of electric power failureas will be apparent.

The energizing circuit for the solenoid valve It includes the mainswitch of valve ill which has one terminal connected by a wire 22 to oneterminal of the secondary of the transformer 20. The other terminal ofthe main switch is connected by a wire 26 to one end of a parallel meshincluded in the circuit.

The parallel mesh comprises an initially closed switch 26, an ignitioncoil 2t and a series resistance element 30 in one branch thereof. Theother branch of the parallel mesh comprises a resistance element 32,which may be designated as a control resistance for the solenoid valveI6 for reasons which will appear hereinafter. The connectionsfor theseelements may be traced from the wire 26 at oneend of the mesh by wayparallel mesh.

of wire 34 to the valve control resistance 32 and thence byway of wire36 to a junction with the wire 38 at the other end of the parallel mesh.The wire 38 connects at one end with the series resistance element 30,the other end of which is connected by a wire 40 to one end of theignition coil 28. The other end of the ignition coil 28 is connected bya wire 46 to one terminal of the nor-. mally closedswitch 26. A wire 48connects the other terminal of the switch 26 to the wire 34 at thejunction thereof with the starting point of the Continuin with theenergizing circuit of the solenoid valve ii, there extends from thejunction of the wires 36 and 38 at one end of the parallel meshpreviously described. a wire 50 which connects by way of a wire 54 withone terminal of the solenoid valve I6. The other terminal of thesolenoid valve I6 is connected by way of a wire 56 to a wire 58 which isconnected with the secondary of the transformer 20. A cut-out,preferably of the slow-acting bimetallic snap switch type, designated bythe numeral 60 may be incorporated in the wire 56 from the solenoidvalve l6 for a purpose which will appear hereinafter.

As desirable in apparatus of the kind described, means are provided topermit the ignition coil 28 to reach igniting temperature before thesolenoid valve 16 opens and permits fuel to flow to the main burner l0.Accordingly, means are provided for shunting the solenoid valve It for aspecified period of time after closing of the main switch of valve l4.-This shunt may be established by a second normally closed switch 62connected in parallel circuit with the valve IS. The connection for thisparallel circuit may be made by a wire 64 connected at one end to thewire 60 and at the other end to one terminal of the switch 62, the otherterminal of the switch being connected by a wire 86 to the wire 58. Aswill be apparent from the schematic view, both the switches 26 and 82form part of a control relay, the actuating coil 88 of which isconnected at one end by a wire to the wire 56 and at the other end by awire 12 to the wire 24. The switches 28 and 62 are similar in that bothopen after a specified time delay, but the switch 28 has a longer timedelay period following closing of the main switch of valve l4. Theseswitches are preferably of the mercury tube type, such as disclosed inPatents Nos. 1,778,439 and 2,224,873 among others, and to which patentsreference may be had for a fuller description. In the present embodimentof this invention, the switch 62 may have a time delay of flve secondsbefore opening and an instantaneous closing, and the switch 26 may openafter a time delay period of thirteen seconds from opening of the switch62 or a total time delay period of eighteen seconds. It is not essentialthat the switch 26 having the longer time delay period also have aninstantaneous closing upon operation of the main switch of valve l4, itbeing only necessary that it assume a closed position before opening ofthe switch 62. Thus, where such a short time delay as five seconds isestablished for the switch 62, then the switch 26 would almostnecessarily have an instantaneous closing action also.

In addition to the shunt for the solenoid valve l6 established by thenormally closed switch 62, an additional shunt is provided for thisvalve. Thus, when the switch 26 having the longer time delay periodopens and causes deenergization of the ignition coil 28, the maintenanceof the solenoid valve in open position is made dependent upon whetherthe resistance of the additional shunt mentioned is of such a value atthis time as to maintain the current through the solenoid valve aboveits release or shut-oi! value. This additional shunt consists of a flamesensitive element or heat responsive device 14 and an adjustingresistance element ll therefor. These elements may be connected inparallel circuit with the valve I8 and cut-out by way of a wire llconnected at one end to the wire 50, and at the other end to one end ofthe flame sensitive element 14. The other end of the element 14 isconnected by a wire 80 to one end of the adjusting resistance element 18and the other end of the element 18 v is connected by a wire 82 to thewire 54. The flame sensitive element 14 may be in the form of a coil ofwire formed from material having normally a relatively low resistanceand a positive temperature coeflicient of resistance. Such elements areknown as ballast resistors and will thus be referred to hereinafter, butother types of flame sensitive or heat responsive devices or thermalresistance elements having the required characteristics may besubstituted.

The purpose of the cut-out 80 in series with the solenoid valve I6 isnow apparent as being for the protection of this valve in the event thatan open circuit occurs in the ballast resistor 14. The excess currentwhich will be diverted to the circuit of the solenoid valve I8 upon suchfailure of the ballast resistor 14 during the normal running period ofthe apparatus will cause the cut-out to operate and open the circuit.During the starting period when the current to the solenoid valve islarge the thermally sensitive element of the cut-out has not becomesufllciently heated to permit the cut-out to operate. Consequently,although at this time there is sufficiently large cur.- rent to thecut-out to cause it to operate, the thermal time lag effectivelyprevents this undesired occurrence. However, upon expiration of thestarting period when the circuit elements are heated, the current to thecut-out is correspondingly reduced and does not increase in the absenceof unusual occurrence; such as open circuiting of the ballast resistor.It will further be apparent that as only the ignition coil 28 and theballast resistor 14 are required to be housed within the chamber 84 ofan oven or like device wherein the burner I0 is situated, there is noexposure of any other elements of the apparatus to the heat or fumesemanating from the burner It.

Further protection is provided for the apparatus in the event of burntout or otherwise damaged parts, by the provision of means to completethe circuit should the ignition coil 28 fail and cause an open circuit.This means takes the form of a manually operated switch 88 which isnormally held open by a spring 88 and is connected in parallel circuitwith the igniter 28. The connections may be traced by way of a wire 20connected at one end to the wire 46 and at the other end to one terminalof the switch 88, and by a wire 92 extending from the other terminal ofthe switch 86 to the wire 40. A suitable electrical resistance element94 may be included in the wire 92 in series with the switch "tocompensate for the loss of the resistance of the ignition coil 28 whenthis coil becomes open-circuited for any cause. a

operation of the device is as follows. Manual or thermostatic closing ofthe main switch of valve [4 effects opening of this valve as describedand permits fuel to flow in the main fuel pipe 82 as far as the solenoidvalve i! which is normally closed. The current from the transformer 20is conducted by the wires 22 and 24 through the main switch to one endof the parallel mesh comprised of the valve control resistor 22, seriesresistance element 30, ignition coil 28 and the time delay switch 28having the long time delay period. From the other end of this parallelmesh the current is conducted by way of the wires 80 and B to theparallel circuit comprising the short time delay switch 82 which shuntsthe solenoid valve it. The circuit from the switch 62 to the transformeris completed by way of the wires 86 and 55, as previously described. Itwill thus be apparent that while the short time delay switch 82 remainsclosed the ignition coil 28 becomes energized and the solenoid valve iiis shunted.

Simultaneously with the energization of the ignition coil 28 theoperating coil 68 of the control relay is also energized through thewires 10 and 72 which extend one from each end of the coil to the wires58 and '24, respectively. Consequentiy, after the specified time delayperiod, which in this instance may be five seconds, the ignition coil 28has reached igniting temperature and the short time delay switch 82opens. The opening of the switch 62 removes the shunt from the solenoidvalve l8 and the current then passes from the wire through the wire towires 82, 80 and 18 which connect these elements to the wires 50 and 58,respectively. As the burner ii) is not yet ignited. the ballast resistorM is unheated and its resistance has consequently not increased. It willbe apparent that the selection of a suitable established value ofresistance for the ballast resistor depends upon the voltage to be usedin the system and may vary in accordance therewith and with the resultssought to be obtained. The resistance of the valve control resistor 32,series resistor 30 and the ignition coil 28 is insufficient to reducethe current flowing to the solenoid valve ii to prevent actuation ofthis valve to open position. Consequently, fuel then passes through thefuel pipe l2 to the burner H) where it is ignited by the ignition coil28.

The flame of the burner I0, if ignited, causes the ballast resistorwhich is exposed thereto to become heated and thus increase itsresistance in response thereto. After suflicient time has elapsed forthe ballast resistor H to become thus heated, which should occur in thespecified time delay of thirteen seconds, the long time delay switch 26opens. The opening of this switch 26 breaks the circuit of the ignitioncoil 28*which, consequently, becomes deenergized. Such operation of thelong time delay switch 26 to open position is entirely automatic andoccurs regardless of whether the ballast resistor is heated or evenwhether. the burner Ill has become ignited. Thus, when the switch 26opens, unless the ballast resistor 14 has become heated and itsresistance increased sufficiently to raise the resistance of the shuntcircuit by an amount to'compensate for the increase in total circuitresistance, then the current through the valve coil will decrease belowholding value and the valve It will close.

It is thus apparent that the determination whether the fuel continues toflow to the burner after the ignition coil 28 is removed from thecircult depends upon whether the burner has previously become ignited.Moreover, ii atany time during operation of the apparatus the flame ofthe main burner i0 ceases, then the ballast resistor will cool and itsresistance be lowered sufficiently to render the current through thevalve coil insuillcient to retain the solenoid vave II in open positionwhereupon this valve will close to I shut oil the fuel supply to theburner.

Operation of the switchof the main valve in an on-off-on cycle willcause the foregoing sequence of events to be repeated due to the resetfeatures of the switches 28 and 62. Thus, a period for purging thevicinity of the main burnor Ill of unburned fuel is provided for atleast as long as the switch 62 having the shorter time delay takes toopen. Since the temperature condition of the ballast resistor 14 doesnot influence the actuation of the solenoid valve I. but only theholding and release of the valve, the circuit need only be adjusted toobtain the proper release current in the valve actuating coil underoperating conditions. Thus, the circuit adjustments are less criticalthan in apparatus where the temperature condition of the ballastresistor is relied upon to actuate and release the valve.

No chattering of the solenoid valve occurs due Ill to the positiveactuation as soon as the first time delay switch opens.

Whereinclusion of a pilot burner is desired then the ignition coil 28and the ballast resistor 14 would be located near the pilot burner flameinstead 01 the main burner flame. The destruction of the ignition coil28 by burning out or other causes need not prevent use of the apparatuswith all the safety features intact. Thus, if the switch 88 is heldclosed while the main switch of valve 14 is moved to closed position,then the fuel flowing from the burner after the short time delay switch82 opens may be lighted with a match. The apparatus will operatethereafter in the same manner as if the ignition coil 28 was fully 1. Asafety control for fuel burners comprising in combination, electricallyoperated means for controlling the supply of fuel to the burner, anenergizing circuit for said controlling means, an electric igniter insaid energizing circuit adapted to produce a flame at the burner, aholding circuit shunting said controlling means, a thermal resistanceelement in said holding circuit adapted clectric igniter adapted toproduce a flame at said burner, a constant resistance element in shuntwith said igniter and connected therewith in series circuit with saidcontrolling means, a thermal resistance element in shunt with saidcontrolling means and adapted to vary its resistance in accordance withthe presence or absence of a flame at said burner, and means fordeenergizing said igniter after said thermal element has had time tovary its resistance, whereby the total resistance bf said circuit isincreased sufiicient to cause said controlling means to shutoil the fuelsupply unless said thermal element has varied its resistance.

3-. A safety control for fuel burners comprising in combination,electrically operated means for controlling the supply of fuel to theburner, an electric igniter adapted to produce a flame at said burner, aconstant resistance element in shunt with said igniter and connectedtherewith in series circuit with said controlling means, a thermalresistance element in shunt with said controlling means and exposed tothe heat of the flame at said burner, said element being adapted toincrease its resistance when heated, and a control relay having a timingdevice for deenergizing said igniter after said thermal element has hadtime to become heated, whereby the total resistance of said circuit isincreased sufficient to cause said controlling means to shut-off thefuel supply unless said thermal element has be come heated.

4. A safety control for fuel burners comprising in combination, anormally closed valve intercepting the supply of fuel to the burner,electrically actuated means for opening said valve, and energizingcircuit for said actuating means,

means in said circuit for igniting said burner cepting the supply offuel to the burner, elec trically actuated means for opening said valve,an energizing circuit for said actuating means, means in said circuitfor igniting said burner upon opening of said valve, heat responsivemeans operative to introduce electrical resistance in shunt with saidvalve opening means in increased amount as said heat responsive meansbecomes heated by a flame at the burner, a control relay having a timingdevice for dee'nergizing said igniting means after said heat responsivemeans has had time to become heated, and a constant electricalresistance element in shunt with said igniting means and operable toincrease the total resistance of said circuit, whereby said valveopening means becomes sufficiently, deenergized upon deenergization ofsaid igniting means to cause closure of said valve unless said heatresponsive means has become fully operative.

6. A safety control apparatus for fuel burners having means forcontrolling the supply of fuel thereto, said apparatus comprising anelectric.

normally closed solenoid valve in series circuit with said igniter andintercepting the fuel supply to the burner, a control relay devicehaving a normally closed switch connected in parallel circuit with saidsolenoid valve, said switch being automatically actuated to openposition but with time delayed action to delay actuation of said valveto open position until said igniter has reached igniting temperature, athermal resistance element connected in another parallel circuit withsaid solenoid valve and exposed to the burner flame, said element beingadapted to increase its resistance when heated, a constant resistanceclement connected in series circuit with said solenoid valve and forminga parallel mesh with said igniter, a second normally closed switchassociated with said relay device and connected in said parallel mesh inseries circuit with said igniter, said second switch being automaticallyactuated to open position but with longer time delayed action than thefirst said switch upon operation of said controlling means to causedeenergization of said igniter after said thermal resistance element hashad time to become heated, said deenergization causing a correspondingincrease in the resistance of the valve energizing circuit sufficient tocause release of said valve to closed position unless said thermalresistance is heated and its resistance increased sufiicient to cause thcurrent through the valve to remain above the holding value of saidsolenoid valve.

'7. In a safety control system for fuel burners having a starting and arunning period, electri cally operable means having an open position forsupplying fuel for combustion by the burner to establish desiredtemperature conditions of the burner, an energizing circuit for saidfuel supplying means including resistance elements so proportioned andarranged that during the starting period sufficient current is suppliedto said fuel supplying means for actuation thereof to open position butduring the running period only sufficient current to maintain saidposition, at least one of said elements being adapted to vary inresistance according to the condition of the burner, and means operablefor opening said circuit upon failure of said variable resistancecausing an increase in current to said fuel supplying means beyond thatrequired during the running period, said means having time-delayedoperation after initial energization and being thereby inoperable toopen said circuit during the starting period.

8. In a safety control for fuel burners, electrically operated means forcontrolling flow of fuel to the burner, an energizing circuit for saidcontrolling means including an electric igniter for the burner, controlrelay means having a timing device adapted to short-circuit saidcontrolling means for a limited period during which said igniter mayreach igniting temperature, and a second timing device associated withsaid relay means and adapted to render said igniter inoperative uponexpiration of a predetermined period following termination of saidshort-circuit period.

9. In a safety control for fuel burners, electrically operated means forcontrolling flow of fuel to the burner, an energizing circuit for saidcontrolling means including an electric igniter for the burner, controlrelay means having a normally closed switch connected in parallelcircuit with said controlling means, said switch being automaticallyactuated to open position upon en.-

ergization of said relay means but with time-delayed action sumcient forsaid igniter to reach igniting temperature, and a, second normallyclosed switch associated with said relay means and connected in seriescircuit with said igniter, said second switch being automaticallyactuated to open position upon energization of said relay but withlonger time-delayed action than the first said switch, said secondswitch being adapted to open the igniter circuit after the first saidswitch has opened to discontinue said parallel circuit.

10. A safety control for fuel burners comprising electrically operatedmeans for controlling flow of fuel to the burner, an energizing circuitfor said controlling means, an electric igniter in said circuit andadapted to produce a flame at the burner, control relay means having anormally closed switch connected in parallel circuit withsaidcontrolling means, said switch being automatically actuated to openposition upon energization of said relay means but with time-delayedaction sufficient for said igniter to reach igniting temperature, asecond normally closed switch associated with said relay means andconnected in series circuit with said igniter, said second switch beingautomatically actuated to open position upon energization of said relaybut with longer time-delayed action than the first said switch, saidsecond switch being adapted to open the igniter circuit after the'firstsaid switch has opened to discontinue said parallel circuit, and athermal resistance element connected in another parallel circuit withsaid controlling means and adapted to vary in its resistance inaccordance with the presence or absence of a flame at the burner, saidresistance element being adapted to cause movement of said controllingmeans upon operation of said second switch in the'absence of a flame atthe burner.

11. A safety control and ignition system for fuel burners having asource of electrical energy, comprising electrically operable means forcon- I trolling the supply of fuel to the burner and being aetuable to afuel supplying position when energy of sufilcient value is suppliedthereto and being movable to a position for preventing said fuel supplywhen energy of insuflicient value is supplied thereto, anelectricigniter adapted when the resistance of said element due to the presence1 or absence of saidflame, and means for establishing a second circuitfor said controlling means effective upon operation of said timingelement for increasing the total circuit resistance to cause saidcontrolling means unless said thermal resistance element is being heatedby said flame.

12. A safety control and ignition system for fuel burners having asource of electrical energy, comprising electrically operable means forcontrolling the supply of fuel to the burner and being actuable to afuel supplying position when energy of sumcient value is suppliedthereto and being movable to a position for preventing said fuel supplywhen energy of insufficient value is supplied thereto, an electricigniter adapted when energized to produce a flame at the burner, a firstcircuit for supplying energy of said sufiicient value to saidcontrolling means and including the source, said controlling means, saidigniter, and a control relay having a timing element operable after apredetermined period for electrically disconnecting said igniter fromsaid circuit, a thermal resistance element having a preselectedtemperature coemcient of resistance located in proximity of the burnerflame and electrically connected to said controlling means for varyingthe energy value supplied thereto upon variations in the resistance ofsaid element due to the presence or absence of said flame, and meansincluding a second resistance element for establishing a second circuitfor said controlling means effective upon operation of said timingelement for increasing the total circuit resistance to cause energy ofsaid insumicent value to be supplied to said controlling means unlesssaid thermal resistance element is being heated by said flame.

13. A safety control and ignition system for fuel burners having asource of electrical energy, comprising electrically operable means forcontrolling the supply of fuel to the burner and being actuable to afuel suppplying position when energy of sufllcient value is suppliedthereto and being movable to a position for preventing said fuel supplywhen energy of insuflicient value is supplied thereto, an electricigniter adapted when energized to produce a flame at the burner, a firstcircuit for supplying energy of said sumcient value to said controllingmeans and including the source, said controlling means, said igniter,and a control relay having a timing element operable after apredetermined period for electrically disconnecting said igniter fromsaid circuit, a thermal resistance element having a preselectedtemperature coeflicient of resistance located in proximity of the burnerflame and electrically connected to said controlling means for varyingthe energy value supplied thereto upon variations in the resistance ofsaid element due to the presence or absence of'said flame, meanseflective upon operation of said timing element for establishing asecond circuit including the source in series with said controllingmeans and thermal resistance element in parallel, and a secondresistance element in series therewith for increasing the total circuitresistance to cause energy of said insufficient value to be supplied tosaid controlling means unless said thermal resistance element is beingheated by said flame.

CHARLES K. STROBEL.

